904 Appendix IL To avoid the evils of varying boiler pressure, a reducing valve is now often used between boiler and cylinder, giving a lower pressure, but steadiness and dryness, Reid's valve, Fig. 864, is a good example. The steam entering at A, finds valve B closed by spring c, so passes along E, and lifting the throttle valve F, acts on the piston D and overcomes the compression of spring c, thus allowing a free flow through D to G at a lower pressure. Now the coiled pipe L is connected to vessel M, which is always full of condensation water, and the low pressure acting on diaphragm N tends to lift lever i and close valve r, thus throttling the pressure on D to the right amount. The lifting tendency is also resisted by the spring H, which can be screwed up against a scale K to give and shew the required reduction. When the hot-well water is returned to boiler, there is danger due to the deposition of cylinder oils on the furnace crowns, causing possible overheating. Feed-water Filters have been there- fore introduced, of which Rankine's, Fig, 865, is an example.